Reinforced gingival retraction cord

ABSTRACT

A gingival retraction cord is constructed from two or more strands that are formed into a plurality of interlocking loops so as to form a knitted retraction cord. At least one strand is made from an absorbent material and another strand is made from a degradation-resistant material such as nylon or polyester. The absorbent strands are impregnated with a hemostatic agent. The degradation-resistant strands resist degradation by the hemostatic agent. Because the strands are part of the knit, the retraction cord is compressible and resilient in the longitudinal and transverse dimensions. Alternatively, one or more strands are used to make the knit and each strand is made from two or more different fibers. For example, one or more absorbent fibers and one or more synthetic fibers can be twisted to make a blended strand. The blended strands can then be used to knit a retraction cord.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates to gingival retraction cords. More particularly, the present invention relates to chemically impregnated retraction cords that have an additional strand or fiber incorporated therein for reinforcing or enhancing the knit of the cord.

2. The Related Technology

When performing various dental procedures, it is often desirable to retract the gingival tissue to prepare the patient's teeth for the procedure. Taking dental impressions, placing crowns, performing bridge work, or effecting other dental restorations are examples of procedures that benefit from retracted gingival tissue. A widely used method for retracting gingival tissue involves the use of retraction cords which are typically braided or knitted for increased strength, flexibility and resilience. Examples of braided or knitted gingival retraction cords may be found in U.S. Pat. No. 4,321,038 to Porteous, U.S. Pat. No. 4,522,933 to Fischer, U.S. Pat. No. 4,617,950 to Porteous et al., and U.S. Pat. No. 4,892,482 to Lococo.

The most common purpose for using a retraction cord is to retract the gingiva away from the tooth to take an accurate and reliable impression of the tooth. It is critical to make an accurate impression of the tooth when constructing artificial crowns to ensure that the crown remains properly secured to the tooth for an extended period of time. It is particularly important to make an accurate impression of the tooth in the area at or below the gingival margin. Failure to take an accurate impression can result in a poorly-formed or deficient prosthesis, particularly at the gingival margin. Premature failure of a crown is often due to poor marginal detail in the impression used to fabricate the crown.

The person's gingiva, or “gums”, not only prevents an accurate impression of the proper shape of a person's tooth beneath the gingiva, it may also bleed if torn or damaged by high speed cutting drills or burrs used to remove tooth material preparatory to placing a crown. This bleeding may further interfere with the taking of a good impression because extravasated blood tends to prevent adequate cleaning and drying of the marginal area of the tooth prior to taking an impression and tends to displace the impression material before it can set. Thus, the dual problems of contraction of the gingival cuff and the presence of hemorrhaging tissues make it impractical to simply take an impression following shaping of the tooth with a high speed drill or burr without retraction of the gingiva.

To control or inhibit the tendency of the gingiva to bleed when physically retracted by the retraction cord and/or if accidentally cut or nicked by the high speed drill or burr, retraction cords are often treated with a hemostatic agent. One type of hemostatic agent includes astringents, which lock or seal off exposed blood vessels so as to arrest bleeding. U.S. Pat. Nos. 4,321,038, 4,522,933, 4,617,950 and 4,892,482, referred to above, discuss the use of astringents such as “alum”, or potassium aluminum sulfate.

Many chemicals used to impregnate a retraction cord often have an adverse affect on the strength of the fibers in the retraction cord. Many retraction cords are made of knitted or braided cotton fibers. The hemostatic agent or astringent placed in the retraction cord can degrade the cord over time making it more likely to fail during use. If fibers in the knit or braid fail during use, the dental packing instrument used to insert the retraction cord into the sulcus can slip through the fibers and potentially cut or injure the underlying tissue. In addition, fragments of the retraction cord can remain embedded between the tooth and gums. Furthermore, the expandability and resilience of the retraction cord diminishes as the integrity of the knit or weave of the cord degrades.

Therefore, what is needed is a gingival retraction cord that can properly retract the gingiva using a hemostatic agent while also resisting decomposition due to the hemostatic agent.

BRIEF SUMMARY OF THE INVENTION

The present invention overcomes the above-mentioned problems by providing a gingival retraction cord that resists degradation when impregnated with an active agent such as a hemostatic agent. According to one embodiment of the present invention, a retraction cord is formed from two or more strands by interlocking a plurality of loops so as to form a knitted retraction cord. At least one of the strands is made from an absorbent material such as cotton. The absorbent strand is impregnated with an active agent such as a hemostat.

At least one other strand in the knit pattern is made from a synthetic or degradation-resistant fiber such as nylon or polyester. The synthetic strand provides the retraction cord with additional structural integrity by resisting degradation caused by one or more active agents.

In an alternative embodiment, the retraction cord of the present invention is formed from one or more strands made from a blend of fibers. One or more absorbent fibers can be twisted together with one or more synthetic or degradation resistant fibers to form one or more reinforced blended strands. The blended strands are then knitted to form the retraction cord of the present invention. In this particular embodiment, each strand of the knit can advantageously include a synthetic or degradation-resistant fiber such that the entire knit resists degradation.

The retraction cord of the present invention may be impregnated with an active agent such as potassium aluminum sulfate, aluminum ammonium sulfate, aluminum sulfate, aluminum chlorohydrate, aluminum acetate, ferric sulfate, ferric subsulfate, ferric chloride, and mixtures thereof. The absorbent strand acts as a carrier for a solution of the active agent. When the retraction cord is packed into the sulcus between the gingiva and a tooth, the active agent is released into the tissue where it arrests bleeding or stiffens the gingival tissue.

The synthetic or degradation-resistant strand gives the retraction cord durability in the presence of the hemostatic agent. As the hemostatic agent breaks down other strands or fibers, the degradation resistant strand resists such degradation thereby preserving the structural integrity of the knit.

The different strands and/or fibers used to make the retraction cord of the present invention are blended together such that each fiber or strand follows the knit pattern. In this way, the blending does not compromise the beneficial features of the knit pattern. Rather, the retraction cord of the present invention is advantageously elastic and resilient in both the longitudinal and transverse dimensions.

Because the retraction cord can expand in the longitudinal direction, the cord can more easily pack into the sulcus between the gingival tissue and the tooth. Areas in the sulcus that require more cord to fill can be filled by compressing the cord longitudinally. Furthermore, as the cord is pushed or pulled in the longitudinal direction the portion of cord already packed in the sulcus is less likely to be disturbed.

Another advantage of the knit pattern of the present invention is that it is resilient in the radial dimension. The strands and fibers in the knit retain a certain level of memory when compressed. As the fibers tend to return to their original position, the gingiva is pushed out radially.

The blend of fiber materials used in the retraction cord of the present invention retains the benefits of the knit pattern by including each fiber in the knit pattern. Blends of absorbent, synthetic, and metal strands or fibers can provide the retraction cord with beneficial characteristics without compromising the benefits derived from the knit pattern.

These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

FIG. 1 illustrates an open-loop configuration used in knitting;

FIG. 2 illustrates a closed-loop configuration used in knitting;

FIG. 3 schematically illustrates the manner in which a single strand of yarn can be knitted using the open-loop configuration of FIG. 1 so as to form a knitted retraction cord from a single strand;

FIG. 4 schematically illustrates the manner in which a plurality of strands may be interlocked and knitted using the closed-loop configuration of FIG. 2 so as to form a knitted retraction cord from several strands;

FIG. 5 illustrates a length of knitted retraction cord formed from four strands according to an exemplary embodiment of the present invention, in which one strand is made from a synthetic material;

FIG. 6 illustrates a transverse cross-section of the knitted retraction cord of FIG. 5 taken along line 6—6;

FIG. 7 illustrates an alternative embodiment of the present invention showing a single strand of the knit being made from a blend of fibers; and

FIG. 8 schematically illustrates a cross-sectional portion of a tooth; the tooth's associated gingival cuff; and a knitted retraction cord being packed into the gingival sulcus between the tooth and the gingival cuff.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

I. Knitted Retraction Cords

As used herein, the terms “knitting” and “knitted” relate to a process of using one or more separate strands to form a series of interlocking loops. A “strand” may include one or more fibers which are twisted or otherwise joined together.

A. Knit Pattern

As shown in FIGS. 1 and 2, two common types of knitting techniques that can be used to form the retraction cords of the present invention include knits made from an “open” loop and a “closed loop.” The “open” loop shown in FIG. 1 is formed using a first loop 10 a that is interlocked with an adjacent loop 12 a such that ends 14 a and 16 a of loop 10 a do not cross one another.

In contrast, FIG. 2 illustrates what is generally known as a “closed” loop knit. The end 16 b of first loop 10 b bends back over and crosses in a manner that closes off the loop 10 b.

FIG. 3 illustrates two rows (generally designated at 18 a and 20 a) of interlocked loops constructed utilizing the open-loop configuration shown in FIG. 1. As seen in FIG. 3, row 18 a includes a plurality of loops 10 a, which are interlocked with loops 12 a of adjacent row 20 a. FIG. 3 illustrates “weft” knitting, which is made from one loop to the next in the same course, or row, of loops, and which can be done using a first strand 21 a for row 18 a and a second strand 21 b for row 20 a. Alternatively, weft knitting can be performed using a single strand or more than 2 strands.

As discussed more fully below, strands 21 a and 21 b are a blend or can include a blend of different materials to give the retraction cord beneficial properties such as resistance to the degrading effects of a hemostatic agent.

FIG. 4, alternatively, illustrates three rows (generally designated at 18 b, 20 b, and 22 b, respectively) of interlocked loops constructed utilizing the closed-loop configuration of FIG. 2. As seen in FIG. 4, row 18 b includes loops 10 b, which are interlocked with the loops 12 b of adjacent row 20 b. Loops 12 b of row 20 b are in turn interlocked with the loops 24 b of adjacent row 22 b, and so on.

FIG. 4 illustrates “warp” knitting in which several strands 26, 28, 30, and 32, are interconnected such that the interlocking loops of each strand connect from one row to the next. As discussed more fully below, the knitted strands can be made of one or more different materials to give the retraction cord advantageous properties.

FIG. 5 shows a gingival retraction cord 34 knitted from four strands 36, 38, 40, and 42 using the closed-loop pattern shown in FIGS. 2 and 4. The number and pattern of strands 36, 38, 40, and 42 is more readily apparent in the cross sectional view of retraction cord 34 illustrated in FIG. 6.

It will be appreciated that the knitted retraction cord of the present invention can be constructed using either an open-loop or a closed-loop pattern or system, as shown in FIGS. 1–5. Retraction cord 34 can also be made using other kitting patterns so long as the knit pattern provides sufficient elasticity and/or resilience. Furthermore, those skilled in the art will recognize that the knit pattern can include any number of strands and each strand can be made from any number of fibers.

B. Strands and/or Fiber Blends

With continued reference to FIGS. 5 and 6, strands 36, 38, 40, and 42 are a blend of strand materials. In an exemplary embodiment, strands 36, 38, and 40 are cotton strands and strand 42 is a synthetic polymer such as nylon or polyester. The blended strands are knitted to form retraction cord 34 having a 3:1 ratio of absorbent to synthetic strands. The blend can be adjusted as desired by using more or fewer absorbent and/or synthetic strands.

In another embodiment, a blended cord material is created by blending two or more fibers to make a strand. One or more strands having blended fibers are then knitted to make a retraction cord. FIG. 7 illustrates an exemplary strand 44 that is made from a blend of cotton fibers 46 a–46 c and a synthetic fiber 48. Fibers 46 a–46 c and fiber 48 are twisted together to form strand 44 having a 3:1 ratio of absorbent to synthetic fibers.

It will be appreciated that strands can be made from more or fewer absorbent fibers and/or synthetic fibers and that the retraction cords of the present invention can have almost any desired blend ratio. Furthermore, blended strands can also be blended with other blended or non-blended strands to create a retraction cord having a desired absorption, resistance to degradation, or resiliency.

Materials used to create the blends of the present invention include natural and synthetic polymers, coated polymers, metal filaments, or any other threadable material that can give the retraction cord a desired property. For instance, cotton can be used for its absorbency, low, cost, and biocompatibility. In one embodiment a polymer fiber or metal filament can be selected to give the retraction cord a desired resiliency, elasticity, or deformability. A metal filament such as silver can also be included to make the retraction cord radiopaque.

In an exemplary embodiment, a synthetic polymer such as nylon or polyester is included in the knit of the retraction cord to resist degradation by an active agent. As discussed below, active agents such hemostatic agents can be included in the retraction cord of the present invention to assist in controlling bleeding of the gingival during a procedure. Typically, active agents break down absorbent fibers such as cotton. In accordance with one embodiment of the present invention, a synthetic polymer such as nylon or polyester is included in the knit to resist degradation and thus failure of the refraction cord. Preventing the failure of the knit helps ensure that the retraction cord properly retracts gingival tissue and reduces the chances that a packing instrument will pierce the knit of the cord and damage the underlying tissue.

As mentioned above, the synthetic or non-degrading material can be blended into the knit through a strand or through individual fibers. In this regard, it can be advantageous to include the non-degrading material as a fiber in each strand of the knit. In this manner, each strand is structurally supported and improved by the blend of fibers.

C. Elasticity and Resilience

The knitted retraction cord 34 of FIGS. 5 and 6 is characteristically highly elastic and resilient in both the longitudinal and transverse dimensions. Each of the strands 36, 38, 40, and 42 used to create the blended cord are formed as part of the knit of retraction cord 34 so as to not disrupt the advantages provided by a knit pattern.

Cord 34 can be easily stretched along its length, and squeezed or compressed radially because of the properties of a knit pattern. In a knitted cord the strand or strands are oriented so that a portion of each strand runs transversely, or at approximately right angles to the longitudinal axis of the cord, thus making the cord more compressible and also more stretchable along its length. In contrast, a twisted-strand or braided-type cord has very little longitudinal or transverse elasticity.

In general, as between twisted-strand or braided-type cords, the use of braided retraction cords has been found to be advantageous over twisted-strand cords because the braided cord better maintains its structural integrity under the force of the dental packing instrument and under the pressure exerted by the surrounding gingival tissue once the cord has been packed into the sulcus.

Surprisingly, the use of a resilient knitted retraction cord has also been found to be more advantageous still in retracting gingival tissue, despite the fact that its inherent elasticity and resilience might be thought to be detrimental by those who have used braided or twisted-strand retraction cords.

Longitudinal elasticity, or the ability to stretch the retraction cord lengthwise, is beneficial because it avoids the tendency for the packed cord to be dislodged as additional cord is pushed into the sulcus between the tooth and the gingival cuff. As the retraction cord is packed, the “stretch” in the knitted cord permits stress to be placed on the cord without causing already packed portions of the cord to be pulled out of the sulcus.

The retraction cord 34 of the present invention is designed to obtain the benefit of having various different materials in the cord, without destroying the benefits of the knit pattern. Unlike attempts in the prior art, the blends of the present invention do not prevent the movement of the cord in the transverse and/or radial dimensions because in the present invention each strand is part of the knit pattern.

II. Active Agents

In an exemplary embodiment, the retraction cord of the present invention includes an active agent such as a hemostatic agent. Hemostatic agents, including astringents and other vasoconstrictors, can be impregnated in the retraction cord to control bleeding and stiffen gingival tissue.

Active agents that may be useful in assisting hemostasis include, but are not limited to aluminum compounds such as potassium aluminum sulfate, aluminum ammonium sulfate, aluminum sulfate, aluminum chlorohydrate, aluminum acetate, other water soluble astringent aluminum salts, and mixtures thereof. Another class of astringents includes iron-based compositions such as ferric salts, including but not limited to ferric sulfate, ferric subsulfate, ferric chloride, and mixtures thereof. Other astringents include permanganates, tannins and zinc chloride. In one embodiment the active agent is a vasoconstrictor such as epinephrine and/or propylhexedrine.

The active agent is typically delivered to the gingival tissue in a solution, such as an aqueous solution. As discussed above, in an exemplary embodiment, retraction cord 34 includes an absorbent material. The absorbent material absorbs the solution thereby impregnating the retraction cord 34 with the active agent. While the active agent may be impregnated using a mechanism other than a solution, a solution is beneficial because it can easily be expressed in the sulcus.

The knitted pattern of retraction cord 34 helps absorb and deliver the active agent. The interlocking loops of the knit pattern substantially increase interstitial volume of cord 34, which allows the retraction cord to carry larger amounts of active agent. Because the knit pattern carries additional active agent, non-absorbent strands can be blended into the knit pattern without affecting the hemostatic ability of the retraction cord.

Additionally, the ability of knitted retraction cords to effectively deliver the active agents to the gingival tissue is greatly augmented by the fact that the knitted retraction cords are compressed when packed in the sulcus. Thus, knitted cords may actually express the hemostatic or other agents into the small capillaries of the gingival tissue when compressed, thereby forcing the active agents into the bleeding pores so as to stop hemorrhage.

III. Method of Use

In FIG. 8, a dental instrument 50 is shown pressing the gingival retraction cord 34 within the sulcus 52 between the gingival cuff 54 and the tooth 56. The resilience and flexibility in the transverse direction allows the knitted retraction cord 34 to conform to irregularities, such as the margin 58 of the tooth 56.

Even if the loops of the knitted retraction cord are left rather loose, because of the intricate interlocking network, there is little or no tendency for the dental packing instrument to slip through the retraction cord. Rather, the compressibility of the knitted cord 34 causes the cord 34 to “dimple” around the edges of the dental packing instrument 50.

Because of the compressibility and bendability of knitted retraction cords there is fewer tendencies for the cords to damage underlying gingival tissue as force is applied during packing. This is because the force of the packing instrument tends to be spread out over a larger area by the interlocking loops of the knitted cord. Also, the transverse resilience of the knitted cord enables it to conform to irregularities within the sulcus. Thus, the knitted cord can accomplish both horizontal and vertical retraction using a single cord.

Another advantage of knitted retraction cords is their tendency to return to their original, uncompressed shape because of their resilience. Thus, when a knitted retraction cord is packed into the sulcus, it is compressed, and the “memory” in the retraction cord causes the cord to gently push outward against the gingival tissue 54. This outward pushing increases the ability of the knitted cord 34 to retract gingival tissues over conventional retraction cords.

Another advantage arising from the compressibility of knitted retraction cords is realized when retracting gingival tissue around the front teeth. The labial gingival tissue is particularly thin and membranous as compared to the lingual gingival tissue. Using the knitted retraction cords of the present invention the lingual gingival tissue can be adequately retracted with the knitted retraction cord only slightly compressed, and by virtue of its compressibility and its ability to stretch and become thinner, the same cord can be packed into the sulcus on the labial side of an interior tooth without over-retracting the gingival tissue. The cord then exerts a general, steady outward force on the tissue, which is desirable.

Another feature of the retraction cord of the present invention is that it can be chemically impregnated with an active agent over an extended period of time without compromising the knit pattern and the benefits that accompany a knitted cord. The synthetic fibers or strands blended into the knit of the retraction cord permit chemical impregnation yet give the retraction cord strength in the event that the active agent degrades other fibers in the cord.

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope. 

1. A gingival retraction cord, comprising: at least one absorbent strand and at least one degradation-resistant strand, the absorbent and degradation-resistant strands being formed into a plurality of interlocking loops so as to form a knitted retraction cord that is deformable; wherein the absorbent strand is entirely comprised of a plurality of fibers that are absorbent; and wherein the degradation resistant strand is entirely comprised of synthetic fibers that are degradation-resistant; and an active agent impregnated within the absorbent strand and wherein the degradation-resistant strand resists degradation by the active agent.
 2. A gingival retraction cord as in claim 1, wherein the fibers of the absorbent strand comprises cotton.
 3. A gingival retraction cord as in claim 1, wherein the fibers of the degradation-resistant strand comprises nylon or polyester.
 4. A gingival retraction cord as in claim 1, wherein the ratio of absorbent strands to degradation strands is 3 to
 1. 5. A retraction cord as in claim 1, wherein the active agent is a hemostat selected from the group comprising aluminum chloride, ferric chloride, ferric sulfate, aluminum sulfate, and combination thereof.
 6. A retraction cord as in claim 1, wherein the active agent is a vasoconstrictor selected from the group consisting of epinephrine, polyhexedrine, and combinations thereof.
 7. A gingival retraction cord, comprising: at least one cotton strand and at least one synthetic strand formed into a plurality of interlocking loops so as to form a knitted retraction cord that is deformable; wherein the cotton strand is entirely comprised of cotton fibers that are absorbent; and wherein the synthetic strand is entirely comprised of synthetic fibers that are degradation-resistant; and a hemostatic agent impregnated within the cotton strand of the knitted retraction cord, wherein the synthetic strand resists degradation by the hemostatic agent.
 8. A gingival retraction cord as in claim 7, wherein the synthetic fibers are comprised of nylon or polyester.
 9. A gingival retraction cord as in claim 7, wherein the hemostatic agent is a hemostat selected from the group consisting of potassium aluminum sulfate, aluminum ammonium sulfate, aluminum sulfate, aluminum chlorohydrate, aluminum acetate, ferric sulfate, ferric subsulfate, ferric chloride, and mixtures thereof. 